1. Field of the Invention
The present invention relates to a switching power supply.
2. Description of the Related Art
In order to generate a voltage that is lower than the supplied input voltage, a power supply circuit such as a DC/DC converter (switching regulator) or the like is employed. Examples of such a known power supply circuit include power supplies using an analog control method and power supplies using a digital control method. With an analog control method, an error amplifier amplifies the difference between the output voltage of the power supply circuit and the target value of the output voltage, and the switching duty ratio is controlled according to the output of the error amplifier, so as to stabilize the output voltage to the target value. With a digital control method, an A/D converter converts the output voltage of the power supply circuit into a digital value, and the duty ratio of a switching transistor is controlled by means of digital signal processing.